The presence of pathogens in the water to be used in medical applications is naturally to be avoided whenever possible. This is especially important in so-called invasive procedures involving a surgical entry into tissues of the patient during various medical and dental treatments. One potential source of serious and sometimes even life-threatening infections can be found in instrument centers, commonly referred to as "dental units," which provide the various instruments, such as drill motors, irrigators, and the like used in dental treatments. The Center for Disease Control and Prevention (CDC) has issued recommendations in effect for the past four years which apply to water to be supplied to dental units during invasive procedures often encountered in dental treatments. (Center for Disease Control and Prevention: Recommended infection-control practices for dentistry, 1993. MMWR 42: No. RR-8:7, 1993.). According to B. G. Shearer in "Biofilm and the dental office," Journal of the American Dental Association, Vol. 127, No. 2, 1996, the American Dental Association has set forth goals for the year 2000 whereby all water delivered to dental patients will have no more than 200 colony forming units (CFU) of live bacteria per cubic milliliter. These recommendations and their application to dentistry are discussed in Waggoner, M. B., "The New CDC Surgical Water Recommendations: Why They Should Be Implemented and What They Require," Compendium, Vol. 17, No. 6, June 1996. As discussed there, dental water line contamination has been a longstanding problem. Various studies have shown bacterial colony-forming unit (CFU) levels in dental unit water lines ranging from 10,000 to 100.times.10.sup.6 CFU per milliliter. This is due to the accumulation of bacterial colonies lining the internal dental unit tubing and the associated delivery tubing. These colonies are known as bacterial biofilms and are relatively resistant to most known biocidal agents. They act as the source for the majority of the bacterial contamination in dental unit water lines. Thus, even if sterile water, such as saline solutions and the like, are supplied to dental units, the water can become contaminated, resulting in the risk of infection to the patient.
Various procedures and treatments are known in the art for controlling various bacterial disease agents in water used for human consumption and in various medical procedures. Chlorination of domestic drinking water has controlled pathogen levels and is, of course, a well established procedure. Even with chlorination, however, a small but acceptable number of bacteria will survive. In several industries, water system design allows accumulation and growth of these few bacteria. This accumulation and growth is exacerbated if the chlorine, which is actually a gas, is allowed to escape from the water while it is not actively flowing. This chlorine loss rapidly occurs through small bore tubing made of plastic, as is commonly seen in dentistry.
Common alternative to chlorination include heavy metals like copper and silver, iodine, ultraviolet light and ozone and ozone-producing products like peroxide. One relatively unexplored approach is the utilization of high concentrations of citrus juice, such as lemon juice or citric acid as discussed in D'Aquino, M., "Lemon Juice as a Natural Biocide for Disinfecting Drinking Water," Bulletin of PAHO 28(4), 1994. Thus, D'Aquino et al discloses, the use of organic acid substances mixed with previously untreated water samples, the substances including natural lemon juice, bottled commercial lemon concentrate, and 7% citric acid solution. Different concentrations of lemon juice and the 7% citric acid solution to natural underground water levels were tested. In general, samples inoculated with the pathogen V-cholerae were not disinfected by 1% lemon juice concentrations in any dilutions resulting in a Ph of 3.9 or higher. As further disclosed by D'Aquino, higher concentrations of 10-25% lemon juice were found to disinfect the water within a period of 5-10 minutes. Lower concentrations down to a minimum of 2% were found to require at least 30 minutes to disinfect the contaminated water. Lemon juice concentrations of 1% or lower were shown to be ineffective.
Various other bactericidal agents, employing both organic and inorganic acids which are useful in forming anti-microbial formulations, are well known in the art. For example, U.S. Pat. No. 4,647,458 to Ueno et al discloses bactericidal agents incorporating mixtures of organic and inorganic acids in alcohol solutions disclosed as useful for bactericides for food stuffs and food processing machines and utensils. Disclosed in Ueno et al are various formulations incorporating organic acids such as lactic acid, acetic acid, tartaric acid, gluconic acid, citric acid, ascorbic acid, malic acid, succinic acid, fumaric acid and phytic acid in combination with various inorganic acids such as phosphoric acid, nitric acid, sulfuric acid, and hydrochloric acid. The salts of such acids also may be employed. The acid or acid salts can be employed in combination with an alcohol, such as ethyl alcohol, in aqueous solutions having a Ph of about 4 or less. U.S. Pat. No. 4,847,088 to Blank discloses an anti-microbial agent comprising a quaternary ammonium silane in combination with an organic acid such as citric acid or maleic acid or an inorganic acid such as boric acid. Various other acids disclosed for use in the Blank formulation include ascetic, adipic, anisic, benzoic, boric, butyric, capric, citraconic, cresotinic, elaidic, formic, fumaric, gallic, glutaric, glycolic, lactic, lauric, levulinic, malic, malonic, oleic, oxalic, palmitic, phthalic, propionic, pyruvic, salicylic, stearic, succinic, tannic, and tartaric acids. The Blank formulations can be used in various carriers to treat substrate surfaces such as carpet fabrics, upholstering, furniture, and the like.
Another application of bactericides is in the treatment of water, such as chlorinated city water and the like, which is applied for use in dental instruments. As discussed in the aforementioned paper by Waggoner, the bacterium Pseudomonas aeruginosa is commonly encountered in water supplied to dental units along with the various other microbes including Burkholderia cepacia, Legionella species, Klebsiella pneumoniae, Staphylococcus species, Streptococcus species, and Escherichia coli. As noted in U.S. Pat. No. 5,158,454 to Viebahn, a singular disinfection and sterilization of the water is ineffective since the infectious microbes are resupplied in the course of the dental operation from the city water or from the patient. In the Viebahn system, a strong oxidant or ozone is incorporated into water in several water reservoirs and passed from there to suitable water supply lines such as those used by a dentist or a dental assistant in the operation of the various dental instruments of a dental unit. The ozone level is maintained initially high to provide the desired disinfectant action in the water while at the same time providing an ozone level which is zero or near zero for the water at the various discharge points where the patient is contacted, such as a syringe or a drill. An ozone detector can be used to sense the ozone level when applied to various end point devices with a signal representative of ozone concentration applied to a control unit which then provides feedback signal for control of the ozone level in a ozone-producing device. Thus, the ozone level is maintained sufficiently high when supplied to one or more water reservoirs to provide for effective control of undesirable microbes and then reduced, if necessary, through the addition of ozone converters as the water is supplied to the various end point devices.
Another system desired to control the presence of infectious microbes in water supplied to dental units is disclosed is U.S. Pat. No. 5,230,624 to Wolf et al. Here, an in-line filter is provided in a supply line leading to a dental instrument, such as a drill or the like, and contains a polyiodide purification resin. The resin functions to neutralize and kill bacteria by the release of iodine from the resin surface to the bacteria through a demand release process involving electrostatic attraction. The resin is positively charged such that the negatively-charged microorganisms are attracted to the resin to the point where iodine is released directly into the microorganism.
Yet another system for delivering treated water to dental handpieces and the like is disclosed in U.S. Pat. No. 5,199,604 to Palmer. In Palmer, a plurality of solution reservoirs are connected through a valved manifold to the inlet side of a peristaltic pump which supplies suitable handpieces, such as an irrigator, for treatment of periodontal disease. By way of example, the various reservoirs may contain colored-coded solutions, such an orange color for a bacteriostatic rinse solution and another color for a hydrogen peroxide solution and various other colors for additional solutions used for irrigation purposes. The peristaltic pump can be employed to deliver the particular irrigating solution selected at a substantially constant pressure and a substantially constant flow rate.
Methods utilized to eliminate bacterial biofilms in industry include steam purging and hyperchlorination "shock treatments." In dentistry, hyperchlorination "shock treatments" have been used, but the "shock treatments" must be repeated every week because the biofilm begins to regrow in that period of time. This type of system also requires use of only sterile water to slow down the biofilm formation. According to J. F. Williams, et al, in "Microbial Contamination of Dental Unit Waterlines: Prevalence, Intensity and Microbiological Characteristics," The Journal of the American Dental Association, Vol. 124, No. 10, 1993, mature biofilms are notoriously resistant to chemical disinfection including these "shock treatments." Thus, if a practitioner does not treat his system for several weeks, the biofilm will become resistant to this method. According to Vess et al in "The colonization of solid PVC surfaces and the acquisition of resistance to germicides by water micro-organisms," Journal of Applied Bacteriology, Vol. 74, No. 2, 1993, most biocidal agents have not been shown to destroy a mature biofilm.